Sanctions squeezed Iran's oil, not its uranium

In the spring of 2025 America's Defense Intelligence Agency judged that Iran could make enough weapon-grade uranium for one bomb in probably less than a week. Twenty-three years earlier, when an exile group revealed a secret enrichment plant at Natanz, Iran had none at all. In between it lived under four UN sanctions resolutions, an EU oil embargo, its banks' expulsion from the world's payment system and seven years of American "maximum pressure". We read 134 reports and updates the International Atomic Energy Agency sent its Board on Iran from 2003 to 2026, figure by figure, to see what each of those did to the programme.

The climb

Iran first enriched uranium to 3.6%, fuel grade, in April 2006. It reached 20% in February 2010, started a second plant buried under a mountain at Fordow in December 2011, and reached 60% in April 2021. In 2023 inspectors found traces of 83.7%, a whisker from the 90% usually called weapon grade, though no stock of it. At the agency's last count, on 13 June 2025, Iran held 9,875kg of enriched uranium, 441kg of it at 60%. Bombing began the same day. The IAEA has not been able to say since how much is left, or where.

Sources: IAEA reports GOV/2006/27, GOV/2010/10, GOV/2012/9, GOV/INF/2016/1, GOV/INF/2019/8, GOV/INF/2021/11, GOV/INF/2021/26, GOV/2023/8, GOV/2015/68, GOV/2025/50; Board resolution GOV/2025/38; press reports

What sanctions did

Sanctions were meant to make the programme too costly to continue. They did make Iran poorer: its crude exports fell from 2.2m barrels a day in 2011 to 1.1m in 2013, and to 0.5m in 2019. They did not make its centrifuges spin slower. We split the years into periods fixed before looking at the numbers and measured, in each, how much enriched uranium Iran made a month.

Under the UN sanctions of 2007-11 Iran made 73kg a month. In 2012-13, as the EU embargo and the banking cut-off halved its oil sales, it made 158kg, twice as much. Across the five periods we can measure, the lower the oil exports, the higher the output. That does not mean sanctions sped the programme up. Iran was installing centrifuges it had built years before, and would probably have run them anyway. But nothing in the IAEA's figures shows the economic squeeze slowing the machines.

What did slow them was a deal. The interim agreement of November 2013 stopped production at 20% and had the existing stock diluted or converted; within nine months it was gone. Output at fuel grade carried on at the same pace. The 2015 deal went further: the stock was cut below 300kg and shipped out, and for more than two years it grew by about 3kg a month. America left the deal in May 2018 and reimposed its sanctions; Iran stayed within the limits for another year, then broke them step by step. From May 2019 to June 2025 its stock grew 57-fold.

There is one more data point, and it predates the sanctions entirely. America's intelligence agencies concluded in 2007 that Iran had stopped work on the design of a weapon in the autumn of 2003, "primarily in response to increasing international scrutiny and pressure resulting from exposure" of its secret work: the revelation of Natanz, not an embargo. The first UN sanctions came three years later.

A year, then a week

The number that matters to the countries watching is the "breakout time": how long Iran would need to make enough weapon-grade uranium for one bomb if it decided to. Before the 2015 deal American officials put it at two or three months. The deal was designed to keep it at a year or more. By 2023 the Pentagon put it at about 12 days, and by 2024 the CIA's director said about a week.

The strikes of June 2025 reset that clock, by how much no one outside governments can check. America's director of national intelligence told the Senate in March that the enrichment programme had been "obliterated" and that Iran had made no effort to rebuild it. Intelligence estimates reported by Reuters in May put breakout at nine months to a year. America's energy secretary said "a small number of weeks". The 441kg of 60% uranium is the difference: if it survived, most of the work is already done.

What is missing

A bomb needs more than fuel. It needs the uranium turned into metal and shaped, a design that works, and a way to deliver it. The public record on each step is thin, and most of it is old.

The gap, in other words, was never mostly technical. America's intelligence agencies said in 2025 that Iran was not building a weapon and that its supreme leader had not reauthorised the programme he suspended in 2003. What stood between a week's worth of fuel and a bomb was a decision.

The fatwa

Iran's government has long said that decision was settled by religion. In August 2005 its delegation told the IAEA's Board that Ayatollah Ali Khamenei had issued a fatwa holding that "the production, stockpiling, and use of nuclear weapons are forbidden under Islam". No written text of such a ruling has been published. In his own words Khamenei mostly called the use of the weapons forbidden; only in 2019 did he say that "building and stockpiling" them was wrong too. A compilation of his rulings published in 2013 did not include it, as critics have pointed out.

It was always a constraint that could be lifted by the man who imposed it. Iran's intelligence minister warned in 2021 that "a cornered cat may behave differently". In 2024 an adviser to Khamenei said that if Iran's survival were threatened it would change its doctrine. In 2024 and 2025 dozens of MPs wrote asking for the doctrine to be reconsidered.

He was killed in a strike on his compound on 28 February 2026, the first day of the war. His son Mojtaba succeeded him in March and has said nothing in public about the ruling that we could find. Others have. On 18 October an MP said that "his fatwa will be different". On 2 November the foreign ministry's spokesman called a change of doctrine "a real issue", because "the other side has assassinated the person who issued the fatwa". The president still says that developing nuclear weapons is forbidden, and in June Iran signed a memorandum with America that "reaffirms that it shall not procure or develop nuclear weapons".

Sanctions cost Iranians dearly, as we found in our first study. On the evidence of the IAEA's own ledger they did not cost the programme much. A negotiated limit did, for three years. Bombs may have, though no inspector has been able to check. What has kept Iran from a weapon so far is the choice not to build one, and the man who made that choice is gone.